An overview of the recent developments in the field of cylindrical vector beams is
provided. As one class of spatially variant polarization, cylindrical vector beams
are the axially symmetric beam solution to the full vector electromagnetic wave
equation. These beams can be generated via different active and passive methods.
Techniques for manipulating these beams while maintaining the polarization symmetry
have also been developed. Their special polarization symmetry gives rise to unique
high-numerical-aperture focusing properties that find important applications in
nanoscale optical imaging and manipulation. The prospects for cylindrical vector
beams and their applications in other fields are also briefly discussed.

Cylindrical vector beams: from mathematical concepts to applications

Imaging systems based on terahertz (THz) time-domain spectroscopy offer a range of unique modalities owing to the broad bandwidth, subpicosecond duration, and phase-sensitive detection of the THz pulses. Furthermore, the possibility exists for combining spectroscopic characterization or identification with imaging because the radiation is broadband in nature. To achieve this, we require novel methods for real-time analysis of THz waveforms. This paper describes a robust algorithm for extracting material parameters from measured THz waveforms. Our algorithm simultaneously obtains both the thickness and the complex refractive index of an unknown sample under certain conditions. In contrast, most spectroscopic transmission measurements require knowledge of the sample's thickness for an accurate determination of its optical parameters. Our approach relies on a model-based estimation, a gradient descent search, and the total variation measure. We explore the limits of this technique and compare the results with literature data for optical parameters of several different materials.

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Material parameter estimation with terahertz time-domain spectroscopy

In this review we propose to address the question: for the life-science researcher, what does X-ray microscopy have to offer that is not otherwise easily available?We will see that the answer depends on a combination of resolution, penetrating power, analytical sensitivity, compatibility with wet specimens, and the ease of image interpretation.

Soft X-ray microscopes and their biological applications

We describe a convenient approach for generating arbitrary vector beams in a 4-f system with a spatial light modulator (SLM) and a common path interferometric arrangement. A computer-generated hologram is introduced onto SLM for performing the beam conversion. Optical realization of a variety of polarization configurations confirms the reliability and flexibility of our method.

Generation of arbitrary vector beams with a spatial light modulator and a common path interferometric arrangement

We introduce the concept of the perfect optical vortex whose dark hollow radius does not depend on the topological charge. It is shown analytically and experimentally that such a vortex can be approximately generated in the Fourier transforming optical system with a computer-controlled liquid-crystal spatial light modulator.

Generation of the "perfect" optical vortex using a liquid-crystal spatial light modulator

We report a 2D static binary phase Dammann vortex grating that combines the features of a conventional vortex grating and a Dammann grating. This grating uniformly distributes energies among the diffraction orders, so the low-efficiency problem at higher diffraction orders of conventional vortex gratings is resolved and the detection range of the optical vortices (OVs) is greatly increased. Experimental results of OV detection using a fabricated 5×5 Dammann vortex grating are given, and the topological charge detection range from −12 to +12 is achieved. The potential applications of such gratings include transmitting, receiving, and multiplexing OV beams in optical communication systems.

Extending the detection range of optical vortices by Dammann vortex gratings

We propose a method for producing a sequence of focused optical vortices along the propagation direction by using a spiral fractal zone plate. The generated beam possesses the optical vortices embedded at subsidiary foci as well as the major ones of the fractal zone plate. The experimental results are obtained in good agreement with the simulations.

Sequence of focused optical vortices generated by a spiral fractal zone plate

As a proof of concept, we experimentally demonstrate multiplexing of free-space optical signals in multiple channels labeled with different states of orbital angular momentum. The multiplexing process is carried out by a dynamic liquid-crystal spatial light modulator, while the phase function is calculated by an iterative algorithm. A binary amplitude computer-generated hologram serves as a demultiplexer.

Multiplexing free-space optical signals using superimposed collinear orbital angular momentum states.

We demonstrate that surface plasmon polaritons can be generated by optical vortex beams at normal incidence focused on a metal surface. The surface plasmon resonant angle can be modulated by the radius of the optical vortex beam in the case of different metal/dielectric interface configurations. Our experiments show that the fluorescence in the vicinity of the metal film surface can effectively be excited and detected within the inner ring of the optical vortex beams due to the localized surface plasmon polaritons.

Surface plasmon polaritons generated by optical vortex beams

We propose a highly efficient approach to generating multihelix beams that contain more than one helical mode, and the power distribution over helical modes is adjustable. A multihelix beam embedded with three collinear helical modes is demonstrated by use of a spatial light modulator.

R. E. Burge

Papers

Extending the detection range of optical vortices by Dammann vortex gratings

Sequence of focused optical vortices generated by a spiral fractal zone plate

Multiplexing free-space optical signals using superimposed collinear orbital angular momentum states.

Surface plasmon polaritons generated by optical vortex beams

Collinear superposition of multiple helical beams generated by a single azimuthally modulated phase-only element